Amyotrophic lateral sclerosis (ALS) and Parkinson's disease (PD) are adult-onset disabling neurodegenerative diseases. While the environmental and genetic causes remain largely unknown, recent studies have identified associations between military service and the risk of developing ALS and PD. Since prospective studies of neurodegenerative diseases such as ALS and PD which have a late age of onset are not usually feasible, further investigation of these associations requires the development of retrospective exposure assessment methods specifically for military occupational and environmental exposures that can be used in community- based case-control studies. The specific aims of this project are: (1) to develop exposure assessment methodology for collecting objective information about military occupations and exposures, and (2) to apply the newly developed methodology to determine whether military service is associated with ALS and PD in three recently completed population-based case-control studies conducted in Western Washington and Northern California. Given their age, a sizable percentage of men in these studies (40%) have served in the military. To address specific aim 1, for subjects who have served in the military, we will construct measures of military occupational and combat exposure using objective data from each subject's record of individual military service, including information on enlistment and discharge dates, military occupational specialty, advanced individual training, transit records, war-zone deployment, duty assignments, and combat medals/badges. Data collection will be carried out blinded to the case-control status of the study subjects, and the completeness and quality of the information will be documented. To address specific aim 2, we will join the data on military service and deployment, with extensive risk factor data obtained from our case-control studies of ALS and PD. All three studies used a case-control design, and together they comprise 360 ALS cases, 584 PD cases and 1376 age- and sex-matched control subjects from the same populations. The studies used similar methodology and identical questionnaires, enabling existing data to be combined and analyzed. Structured interviews were used to collect extensive information on demographic factors, clinical characteristics, occupational exposures, lifestyle behaviors and other potential risk factors for ALS and PD. The studies include information on lifetime residence history as well as lifetime job history, including information on military service and deployment, locations of service, and duration of service. Identifying the occupations and exposures that are associated with a higher risk of neurodegenerative diseases will provide important clues to their etiology and provide opportunities for future prevention. PUBLIC HEALTH RELEVANCE: Project Narrative Recent studies have found that men who served in the military have a two-fold increased risk of developing neurodegenerative diseases, amyotrophic lateral sclerosis (ALS) and Parkinson's disease (PD), compared to men who never served in the military. The primary objective of this study is to develop exposure assessment methods for occupational exposures in military occupations and at times of war deployment, and to apply these methods with data from three completed epidemiologic studies to determine whether these exposures increase the risk of developing neurodegenerative diseases (ALS, PD). By developing methodology for collecting and analyzing data about putative military occupations and exposures, methods developed as part of the proposed research would also enable further study of military risk factors by two large research consortia in North America (for ALS and PD).